1. Field of the Invention
The present application relates to the use of the characteristics of an ion current sensor signal for onboard measurement of engine emissions such as NOR, CO, CO2, unburned hydrocarbon (HC), excess O2 in the exhaust and for onboard measurement of cylinder pressure and temperature and for the control of different engine parameters accordingly.
2. Description of Related Art
One existing technology in measuring NOx emissions utilizes a chemiluminescence detector (CLD) that samples gases to a chamber full with ozone (O3), where the chemical reaction between NO and O3 takes place producing luminescence proportional to the NO concentration. The CLD method is used only in research or during engine calibration and development as it requires very expensive instrumentation and maintenance. Another existing technology a sensor located in the exhaust pipe or with after treatment device which consists of Zirconia multilayer ceramics in metal housing. The NOx concentration in the exhaust gas is proportional to the electrical current controlling the electro-chemical pumps that adjusts the oxygen concentration in the cavities of the sensing element. The problem of this type of sensor is their slow time response and low sensitivity, and it requires recalibration due to signal drafting. Further, this type of sensors is unable to predict the concentration of NOx attributable to each engine cylinder accurately. This brings us to the conclusion that there is no in-cylinder, low cost technology that is capable of quantitatively and adequately predict the concentration of NOx produced in internal combustion engines.
Regarding CO, CO2, and unburned hydrocarbon (HC), there is no in-cylinder onboard sensor available to predict these emissions produced by the engine. As for excess O2 in the exhaust, one known sensor is the lambda sensor which is currently used by the auto industry. However, the use of the ion current sensor to predict excess O2 is a faster technology as the predictions are based on a cycle by cycle basis.
For cylinder pressure and temperature, pressure transducers are considered for this type of measurements. As cylinder pressure is measured and cylinder temperature is then calculated from the pressure trace. This is a reliable technology, however, the cost of a pressure transducer is still high compared to the use of the ion current sensor to predict cylinder pressure and temperature.